After medical pot use was made legal in California in 1996, Mills says, per-person residential electricity use in Humboldt County jumped 50 percent compared to other parts of the state.

In order to produce some 17,000 metric tons of marijuana this year, Mills estimates authorized growers will use $5 billion worth of energy. That works out to the output of seven big electric power plants.

Much of the carbon dioxide produced by the industry comes from transportation, though the need for lights “500-times greater than recommended for reading” also uses a lot of power and generates a lot of pollution. Air conditioning, ventilation and humidity control also contribute.

In California, some 400,000 authorized growers use about 3 percent of the state’s electricity for their business.

“This corresponds to the electricity use of 1 million average California homes, greenhouse-gas emissions equal to those from 1 million average cars, and energy expenditures of $3 billion a year,” Mills says. However, since California is such a green state, it only generates 20 percent of national carbon dioxide emissions from pot growing, while using 70 percent of nationwide energy for this industry.

“From the perspective of individual consumers, a single Cannabis cigarette represents 2 pounds of (carbon dioxide) emissions,” Mills says.

For this report, which he published independently, Mills says he didn’t count the energy used in producing fertilizer, water, equipment and building materials also used in indoor pot farms.